Coloration of hair is a procedure practiced from antiquity employing a variety of means. In modern times, the method most extensively to color hair is an oxidative dyeing process utilizing one or more oxidative hair coloring agents in combination with one or more oxidizing agents.
Most commonly a peroxy oxidizing agent is used in combination with one or more oxidative hair coloring agents, generally small molecules capable of diffusing into hair and comprising one or more primary intermediates and one or more couplers. In this procedure, a peroxide material, such as hydrogen peroxide, is employed to activate the small molecules of primary intermediates so that they react with couplers to form larger sized compounds in the hair shaft to color the hair in a variety of shades and colors.
A wide variety of primary intermediates and couplers have been employed in such oxidative hair coloring systems and compositions. Among the primary intermediates employed there may be mentioned p-phenylenediamine, p-toluenediamine, p-aminophenol, 4-amino-3-methylphenol, N,N-bis(2-hydroxyethyl)-p-phenylene diamine, 1-(2-hydroxyethyl)-4,5-diaminopyrazole and as couplers there may be mentioned resorcinol, 2-methylresorcinol, 3-aminophenol, 2,4-diaminophenoxyethanol, and 5-amino-2-methylphenol.
There are numerous additional requirements for oxidation dye compounds that are used to dye human hair besides the color or the desired intensity. Thus, the dye compounds must be unobjectionable in regard to toxicological and dermatological properties and must provide the desired hair color with a good light fastness, fastness to a permanent wave treatment, acid fastness and fastness to rubbing. The color of the hair dyed with the dye compounds in each case must be stable for at least 4 to 6 weeks to light, rubbing and chemical agents. Furthermore, an additional requirement is the production of a broad palette of different color shades using different developer and coupler substances. Many of the desired shades have been produced with dyes based on p-aminophenol. However, as indicated in U.S. Pat. No. 4,997,451, the use of p-aminophenol is being questioned, for possible toxicological reasons. The proposed replacements for p-aminophenol have not proved entirely satisfactory. There is therefore a need for new primary intermediate compounds to meet one or more of the desired properties but not possessing the possible toxicological drawbacks possessed by p-aminophenol.